Residual photoelastic method

Residual stresses of PS parts with 1mm thickness have been investigated by photoelastic method. It is found that processing parameters different influence the magnitude of residual stresses, according to its contribution ranked as melt temperature, packing pressure, and injection velocity. Improve melt temperature and lower packing pressure benefit to decrease residual stress. Incompetent injection molded parts usually have high... 

The photoelasticity method can only apply to amorphous materials which have very good birefringent properties, such as polycarbonate. Experiment is used to observe the stress distribution, judge the high stress area and determine the value of residual stress [9]. 

Residual stresses of PC parts have been investigated by numerical and photoelastic method. It is found that flow-induced residual stresses are main cause in thin part while thermal-induced residual stresses are main cause in thick part. 

This photoelastic stress analysis is a technique for the nondestructive determination of stress and strain components at any point in a stressed product by viewing a transparent plastic product. If not transparent, a plastic coating is used such as certain epoxy, polycarbonate, or acrylic plastics. This test method measures residual strains using an automated electro-optical system. 

An independent method of determining stress, especially useful for materials under flow, is from the optical birefringence. Of course, it is limited to transparent materials, which precludes application to filled polymers. Because of the need for transparency, stress birefringence has been used more often for plastics than rubber. Residual anisotropy due to unrelaxed orientation can also be assessed using birefringence this is commonly known as the photoelastic effect. Generally the birefringence is directly proportional to the tme stress... 

ASTM C 978 - 04, Standard Test Method for Photoelastic Determination of Residual Stress in a Transparent Glass Matrix Using a Polarizing Microscope and Optical Retardation Compensation Procedures... 

Experimental work [118-125], especially that using photoelastic techniques, has established the presence of residual stresses in joints but the results have often not been quantitative. For the simpler case of polymeric films coated onto metallic substrates, photoelastic techniques and a method based upon the bimetallic strip principle have often been employed [126-131]. Using the latter method, Danneberg [130] showed that for a wide range of epoxy-based coatings on an aluminium substrate thermal contraction was a major cause of internal stress and that the stresses generated were of the order of 0.08... 

The present study combines photoelastic experiments and numerical methods to investigate residual stresses in injection molded polycarbonate samples. There are two types of samples are measured to verify the criterion is valid. Numerical simulations are used to separate thermal-induced stresses and flow-induced stresses, while experiment results are used for comparison. Software named PARTMOLDING in which governing equations include viscoelastic fluid model is developed to calculate flow-induced residual stress mainly. Thermal-induced stresses are simulated by MOLDFLOW MPI5.0. Compared with experiments, it is found that the criterion is helpful to choose appropriate simulation theory, improve simulation precision and reliability. 

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